1. Field of the Invention
This invention relates to an inertial energy storage device employing a non-rigid flywheel.
2. Description of the Prior Art
There is presently a great and long sought need for efficient and long lasting energy storage devices. Inertial energy storage devices appear to have the capability of meeting this need.
One of the requirements of inertial energy devices such as flywheels is that they have high tensile strength per unit of mass. The energy stored in a flywheel is linearly proportional to the mass of the flywheel and proportional to the square of the angular velocity of the flywheel. A flywheel of this nature can store ten times as much energy as an electric battery of the same weight.
Composite flywheels of synthetic materials are well known. Flywheels fabricated from those fibers bonded by a resin, however, have proved to have problems with delamination and subsequent catastrophic failure. Such a failure is caused by the fact that the fibers and the resin have different elastic properties which causes delamination due to different expansion under stress.
The Wetherbee (U.S. Pat. No. 3,602,067) and Reinhart (U.S. Pat. No. 3,296,886) patents both disclosed flywheels made of laminated plastics while the Call (U.S. Pat. No. 3,496,799) patent discloses a flywheel of homogeneous metallic material. All of these designs employ a rigid material whereas the present invention uses non-rigid material. The desired rigidity of the present invention is caused by centrifugal force alone. By using non-rigid materials, the present invention greatly reduces the amount of vibration which can be transmitted from the flywheel to the shaft due to its non-rigid suspension thereby greatly increasing the lifetime of the inertial energy storage device.
Another disadvantage of existing inertial energy storage devices employing rigid material is their inherent propensity towards catastrophic failure. Such a catastrophic failure could be especially bad should it occur in a moving vehicle. The sudden great torque applied to the vehicle frame by such a failure could cause the vehicle to go out of control. The present invention, on the other hand, is designed to prevent such a catastrophic failure. The Seeliger patent (U.S. Pat. No. 3,662,619) discloses a fail-safe rotating machine wherein predetermined failure locations are designed into the rotating element to assure minimum energy release upon failure of the element due to the centrifugal forces acting thereon. More specifically, a cylindrical flywheel mounted on a motor shaft is formed of juxtaposed discs having varying tensile strengths to inhibit simultaneous failure of the discs. Should any one disc fracture, the fractured segment would be free to be thrown from the flywheel by centrifugal force. The dislodged segment then tends to inhibit rotary motion of the motor by welding to the interior surface of the flywheel shield and jamming between the periphery of the flywheel and the interior of the shield. such a catastrophic failure might seriously damage both the remaining portion of the flywheel and, perhaps more seriously, the adjacent electric motor.
In the present invention, an element of the flexible material comprising the flywheel is of a lesser tensile strength than the remaining material. For example, one or more strands of rope, or parts thereof, will be of lesser tensile strength than the rest of the rope. The element of lesser tensile strength is used merely as a probe and its mass is but a small percentage of the flywheel mass. The probe element will be activated before a catastrophic failure occurs and its failure does not constitute a catastrophic failure. Its failure allows a braking fluid to rush into a sealed vacuum chamber containing the flywheel so that catastrophic failure of the flywheel is prevented by the braking action of the fluid. Seelinger, on the other hand, attempts to minimize the consequences of the catastrophic failure after it has occurred.
Energy storage devices of the flywheel type are also disclosed in U.S. Pat. No. 3,208,303 to Durouchoux and U.S. Pat. No. 3,368,624 to Clerk.